Innovative combinational closed-loop and open-loop satellite user terminal power control system

ABSTRACT

Devices and methods are disclosed for reducing power control cushion of a user terminal configured to communicate with a satellite and a gateway station. The present invention provides a power control algorithm implemented in a user terminal that is designed to operate in a satellite communication system. The power control algorithm can recursively calculate a returnlink power to reduce a power control cushion so that an extra link margin is available to the satellite communication system. The present invention also provides a source coding technique that provides an accurate feedback signal for the user terminal. The average metric of input signal frames is coded in a sequence of bits that are carried by contiguous output signal frames.

BACKGROUND OF THE INVENTION

The present invention generally relates to a wireless communicationsystem and, more particularly, to a user terminal power control systemwith a predictive closed-loop and adaptive correlation open-loopapproach.

There are presently many different types of radiotelephones or wirelesscommunication systems, including different terrestrial based wirelesscommunication systems and satellite communication systems.

The CDMA2000, an exemplary cellular system, is a communication protocoland specifies the technical requirements that form a compatibilitystandard for CDMA systems. One of the technical requirements specifiedin CDMA2000 is allocating one bit per data package (or, equivalently,frame) to specify the status of signal power strength. FIG. 1 isschematic diagram of a typical terrestrial wireless communication system100, where user terminals 104, such as cellular phones, Personal DigitalAssistants (PDAs), etc., communicate with each other via a gatewaystation 102.

In the communication system 100, each user terminal 104 exchanges a datapackage (or, equivalently, frame) with the base station 102 at each timeinterval that is about 20 milliseconds in CDMA2000 system. To conform tothe CDMA2000 requirements, each data package contains one bit dedicatedto indicate the received signal quality (or, equivalently, transmissionpower level). The data contained in the one bit may be used by thereceiver to adjust the transmission power level of the following datapackage. Thus, one cycle of data exchange makes a closed feedback loopto adjust the transmission power levels of the communicating userterminals 104. The adjustment of signal level is required to minimizethe interference between the user terminals 104 and, consequentlyenhance the quality of communications therebetween. A weak signal levelfails to provide clear communication between each user terminal 104 andthe base station 102, while an excessively strong signal from one userterminal may produce an undesirable interference to other userterminals. As the power control cannot be perfect, for eachcommunication system design, some additional power allowance is placedto allow the power control error. The additional power allowance isknown as power control cushion. It is clear that for power useefficiency and for system reaching a high performance and high capacitylevel, the power control cushion should be as small as possible.

In the terrestrial wireless communication system 100, the time delay ofthe closed feedback loop can be just a matter of tens of millisecondsand, as a consequence, the closed feedback loop power control canpromptly adjust its power level to adapt the environmental change. Incontrast, the time delay of the closed-loop methods for existingsatellite communication systems can be significant. For example, in atypical GEO satellite communication system, the feedback closed-loopdelay is about ¼ second for a single hopping method and about ½ secondfor a double hopping method. With such a long feedback time delay, awell-designed conventional closed-loop method by itself may fail toprovide a satisfactory power control and at least a 2-dB power controlcushion is required.

In the design of a satellite system, closing the link budget whileproviding the largest possible transmission capacity has been achallenging problem to engineers. In addition, the transmission powerlimitation may compound the difficulty of the problem. Analysis showsthat in a GEO Mobile system, with other resources the same, a reductionof the power control cushion by 1-dB can double the system capacity.

Therefore, there is a need to complement the long loop delay effect inthe power control system so that the power control cushion can bereduced and, consequently, the system capacity can be increased and thequality of service can be enhanced.

SUMMARY OF THE INVENTION

The present invention provides an innovative communication system powercontrol architecture for a communication system with long transmissiondelay. The proposed system architecture uses the conventionalclosed-loop power control scheme as well as open-loop power controlscheme. The migrated results of the closed-loop and the open-loopcontrol schemes are used to effectively reduce the required powercontrol cushion. This architecture includes the algorithms for userterminals, for satellites and/or gateway station, and the coordinationbetween the user terminals and a satellite and/or gateway station.

The present invention also provides a power control algorithmimplemented in a user terminal that can communicate with a satellite anda gateway station in a real-time basis. The power control algorithm canrecursively calculate a returnlink power to reduce a power controlcushion so that the system capacity and system performance of thedesigned satellite communication system can be improved. The presentinvention also provides a source coding technique that provides anaccurate feedback signal for the user terminal. The average metric ofinput signal frames is coded in a sequence of bits that are carried bycontiguous output signal frames.

In one aspect of the present invention, a method for coding an averagemetric value of a plurality of input signal frames includes steps of:receiving a plurality of input signal frames; decoding the plurality ofinput signal frames; calculating a plurality of metrics using theplurality of input signal frames; calculating an average metric of theplurality of metrics; selecting a sequence of bits comprising aplurality of synchronization bits and a set of information bits;populating the sequence of bits, the set of information bitscorresponding to the average metric; and sending the sequence of bitsusing a plurality of output signal frames.

In another aspect of the present invention, a computer readable mediumembodying program code with instructions for coding an average metricvalue of a plurality of input signal frames includes: program code forreceiving a plurality of input signal frames; program code for decodingthe plurality of input signal frames; program code for calculating aplurality of metrics using the plurality of input signal frames; programcode for calculating an average metric of the plurality of metrics;program code for selecting a sequence of bits comprising a plurality ofsynchronization bits and a set of information bits; program code forpopulating the sequence of bits, the set of information bitscorresponding to the average metric; and program code for sending thesequence of bits using a plurality of output signal frames.

In still another aspect of the present invention, a method forcontrolling a returnlink power of a user terminal includes steps of:receiving a broadcasting-signal-to-noise-ratio; estimating a forwardlinkcarrier-signal-to-noise-ratio based on thebroadcasting-signal-to-noise-ratio; predicting a forwardlink degradationbased on the forwardlink carrier-signal-to-noise-ratio; receiving anerror of a returnlink signal; estimating a returnlinkcarrier-signal-to-noise-ratio based on the error; predicting a noise andinterference of the returnlink signal; and calculating a returnlinkpower signal based on the forwardlink degradation, noise andinterference.

In yet another aspect of the present invention, a computer readablemedium embodying program code with instructions for controlling areturnlink power includes: program code for receiving abroadcasting-signal-to-noise-ratio; program code for estimating aforwardlink carrier-signal-to-noise-ratio based on the receivedbroadcasting-signal-to-noise-ratio; program code for predicting avariation of forwardlink degradation based on a variation of theforwardlink carrier-signal-to-noise-ratio; program code for receiving anerror of a returnlink signal; program code for estimating a returnlinkcarrier-signal-to-noise-ratio based on the received error; program codefor predicting a noise and interference of the returnlink signal; andprogram code for calculating a returnlink power signal based on theforwardlink degradation, noise and interference.

In another aspect of the present invention, a satellite communicationsystem includes: a satellite; and at least one user terminal comprising:a forwardlink receiver configured to receive a forwardlink broadcastingsignal and a forwardlink user-data transmission signal from thesatellite; a returnlink power control configured to generate areturnlink power signal based on the forwardlink broadcasting signal andthe forwardlink user-data transmission signal; and a returnlinktransmission configured to send the returnlink power signal to thesatellite.

In another aspect of the present invention, a satellite communicationsystem includes: a satellite; at least one user terminal configured tocommunicate with the satellite via a channel, the at least one userterminal comprising: a forwardlink receiver configured to receive aforwardlink broadcasting signal and a forwardlink user-data transmissionsignal from the satellite; a returnlink power control configured togenerate a returnlink power signal based on the forwardlink broadcastingsignal and the forwardlink user-data transmission signal; and areturnlink transmission configured to send the returnlink power signalto the satellite; and a gateway station configured to communicate withthe satellite comprising: a feederlink receiver configured to receive asignal from the satellite; and a feederlink transmission configured toreceive a metric and a pilot tune signal power from the feederlinkreceiver and send a signal to the satellite.

In another aspect of the present invention, a method for coding anaverage metric value of a plurality of input signal frames includessteps of: receiving a plurality of input signal frames; decoding thereceived plurality of input signal frames; calculating a plurality ofmetrics using the decode plurality of input signal frames; calculatingan average metric of the calculated plurality of metrics; coding thecalculated average metric; and sending the coded average metric using aplurality of output signal frames.

In another aspect of the present invention, a method for coding anaverage metric value of a plurality of input signal frames includessteps of: receiving a plurality of input signal frames; decoding thereceived plurality of input signal frames; calculating a plurality ofmetrics using the decode plurality of input signal frames; calculatingan average metric of the calculated plurality of metrics; selecting asequence of bits comprising a plurality of synchronization bits and aset of information bits; assigning ones to the plurality ofsynchronization bits; populating the set of information bits inaccordance with the average metric; and sending the populated sequenceof bits using a plurality of output signal frame.

In another aspect of the present invention, a method for controlling areturnlink power of a user terminal includes steps of: receiving abroadcasting-signal-to-noise-ratio; estimating a forwardlinkcarrier-signal-to-noise-ratio based on the receivedbroadcasting-signal-to-noise-ratio; predicting a forwardlink degradationbased on the estimated forwardlink carrier-signal-to-noise-ratio;receiving an error of a returnlink signal; estimating a returnlinkcarrier-signal-to-noise-ratio based on the received error; predicting anoise and an interference of the returnlink signal; calculating areturnlink power signal based on the predicted forwardlink degradation,the predicted noise level, and the predicted interference level; usingthe calculated returnlink power signal in the steps of estimating areturnlink carrier-signal-to-noise-ratio, predicting a forwardlinkdegradation, and predicting a noise and an interference; and estimatinga set of model parameters to adjust the noise, interference, and adynamic degradation based on an adaptive filter such as a Kalman filter.

In another aspect of the present invention, a method for controlling areturnlink power of a user terminal includes steps of: receiving areturnlink error and a returnlink power; estimating a returnlinkcarrier-signal-to-noise-ratio based on the returnlink error andreturnlink power; predicting a noise and interference of the returnlinkpower based on the returnlink carrier-signal-to-noise-ratio and thereturnlink power; receiving a forwardlink power; estimating aforwardlink carrier-signal-to-noise-ratio based on the forwardlinkpower; calculating adaptively a correlation between a variation of theforwardlink power and a variation of the returnlink power; predicting aforwardlink degradation based on the forwardlinkcarrier-signal-to-noise-ratio, the correlation and the returnlink power;and computing a returnlink power based on the noise, the interferenceand the forwardlink degradation.

In another aspect of the present invention, a computer readable mediumembodying program code with instructions for controlling a returnlinkpower includes: program code for receiving a returnlink error and areturnlink power; program code for estimating a returnlinkcarrier-signal-to-noise-ratio based on the returnlink error andreturnlink power; program code for predicting a noise and interferenceof the returnlink power based on the returnlinkcarrier-signal-to-noise-ratio and the returnlink power; program code forreceiving a forwardlink power; program code for estimating a forwardlinkcarrier-signal-to-noise-ratio based on the forwardlink power; programcode for calculating adaptively a correlation between a variation of theforwardlink power and a variation of the returnlink power; program codefor predicting a forwardlink degradation based on the forwardlinkcarrier-signal-to-noise-ratio, the correlation and the returnlink power;and program code for computing a returnlink power based on the noise,the interference and the forwardlink degradation.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a conventional terrestrial wirelesscommunication system;

FIG. 2 is a schematic diagram of a satellite communication system inaccordance with one embodiment of the present invention;

FIG. 3 is a schematic diagram illustrating a power control informationflow between components of the communication system of FIG. 2;

FIG. 4 is a schematic diagram illustrating a returnlink power controlconcept of the communication system of FIG. 2;

FIG. 5 is a functional block diagram illustrating a returnlink powercontrol algorithm in accordance with one embodiment of the presentinvention, which is further illustration of 418 showing in FIG. 4;

FIG. 6 is a schematic diagram illustrating an exemplary metric feedbacksource coding in accordance with one embodiment of the presentinvention;

FIG. 7 is a plot of BER vs. carrier-signal-to-noise-ratio illustratingan effect of a channel decoding in accordance with one embodiment of thepresent invention;

FIG. 8 is a plot of measured and averaged signals in accordance with oneembodiment of the present invention;

FIG. 9A is a plot of signals illustrating the effect of a power controlon an error signal in accordance with one embodiment of the presentinvention;

FIG. 9B is a plot of carrier-signal-to-noise-ratio distributions inaccordance with one embodiment of the present invention;

FIG. 10 is a flowchart illustrating exemplary steps for metric feedbacksource coding in accordance with one embodiment of the presentinvention.

FIG. 11 is a flowchart illustrating exemplary steps for controlling thereturnlink power of a user terminal in accordance with one embodiment ofthe present teachings.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out the invention. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the invention, since the scope of theinvention is best defined by the appended claims.

Broadly, the present invention provides an algorithm to reduce areturnlink power control cushion so that an extra link margin isavailable to a satellite communication system, where the extra linkmargin can enhance the capacity of the system and quality of theservice. In contrast to the existing systems, the present inventionimplements an open loop estimation model as well as the closed loopmodel to control the transmission power. (Hereinafter, the term“returnlink” refers to sending a signal to a satellite.) In addition,the present invention provides a source coding technique that providesan accurate feedback signal for a user terminal.

FIG. 2 is a schematic diagram of a satellite communication system 200 inaccordance with one embodiment of the present invention. As illustratedin FIG. 2, the system 200 may include: user terminals 204, such asPersonal Digital Assistants (PDAs) or cellular phones; a satellite 202(or, equivalently, a spacecraft); and a gateway station 206. Forsimplicity, only two user terminals and one gateway station are shown inFIG. 2. However, it should be apparent to those of ordinary skill thatthe present invention may be practiced with any number of user terminalsand gateway stations. Each of the user terminals 204 and the gatewaystation 206 may send a communication signal to the satellite 202.Hereinafter, the term “forwardlink” refers to sending a signal to thegateway station 206 or user terminal 204. Likewise, the satellite 202may send a communication signal to each of the user terminal 204 and/orthe gateway station 206.

FIG. 3 is a schematic diagram 300 illustrating a power controlinformation flow between the components of the communication systemshown in FIG. 2. As indicated by arrows 304 a and 304 b, the returnlinktransmission 322 of a user terminal 204 may send a signal to thereturnlink receiver 306 of a satellite 202 through a channel 302. Then,the returnlink receiver 306 may send the received signal to a feederlinktransmission 308 as indicated by an arrow 304 c. The feederlinktransmission 308 may pack a set of similar signals from other userterminals 204 and send the packed signal to the feederlink receiver 310of the gateway station 206 as indicated an arrow 304 d. Upon receipt ofthe packed signal, the gateway station 206 may unpack the receivedsignal and process the unpacked signal prior to sending to a feederlinktransmission 312 as indicated by an arrow 304 e, where the process mayinclude the steps of evaluating the intensity level of each signal andadding a returnlink channel decoding metric Metric_(R) and atransmission power for pilot tune (or, equivalently, broadcasting)signal Power_(FP) (or, briefly P_(FP)) to the unpacked signal.Hereinafter, the subscript “R” and “FP” refer to the returnlink and theforwardlink pilot tone signal (or, equivalently, a broadcasting signalfrom the satellite 202). The value of Metric_(R) may be carried by onebit per frame and indicate the intensity level of a returnlink signalthat is sent by the user terminal 204 to the satellite 202. TheMetric_(R) may be available when the returnlink information is processedand may have a time delay as will be explained later. The P_(FP) may beconsidered as a constant or a slowly changing quantity for most of thecommunication systems. Thebroadcasting-signal-to-noise-and-interference-levelS_(FP)/(N_(FP)+I_(FP)) may be measured at the user terminal 204. Also,the broadcasting signal change may be considered as a change in thedegradation of the channel 302, which may be used for an open-loop powercontrol. Details of the open-loop power control will be given later.

As indicated by an arrow 304 f, the feederlink transmission 312 may senda processed signal to the feederlink receiver 314 of the satellite 202.Then, the feederlink receiver 314 may send the received signal to aforwardlink transmission 316 that can be an antenna, as indicated by anarrow 304 g. Subsequently, the forwardlink transmission 316 may send twosignals: a forwardlink broadcasting signal and forwardlink user-datatransmission signal as indicated by arrows 304 h and 304 j,respectively. Typically, the forwardlink broadcasting signal may be sentto every user terminal 204. These two signals may go through the channel302 and be received by a forwardlink receiver 318 as indicated by arrows304 i and 304 k. The forwardlink receiver 318 may decode the receivedsignals and make some measurements before sending the decoded signal toa returnlink power control 320 as indicated by an arrow 304 l. Then, asindicated by an arrow 304 m, the returnlink power control 320 may sendthe information of a returnlink transmission power P_(R) to thereturnlink transmission 322.

The flow chart 300 shows a double hopping closed-loop satellitecommunication system. In an alternative embodiment, a single hoppingclosed-loop satellite communication system may be used, wherein thegateway station functionality can be performed by the satellite 202.

The channel 302 may include two types of degradation mechanisms: adynamic channel degradation 324 that may occur close to the userterminal 204 due to atmospheric and/or environmental impacts; and astatic channel degradation 326 in the out-space region. From the timedelay and time prediction point of view, using the forwardlink signalsthat are sent by the forwardlink transmission 316 to estimate thedynamic channel degradation 324 may create a short time delay whileusing the returnlink feedback closed-loop as defined by the arrows 304a-304 m may create a long delay (¼ second for single hopping and ½second for double hopping).

As mentioned, the return power P_(R) may represent the power level of asignal that the user terminal 204 sends to the satellite 202 and beadjusted on a regular basis by the user terminal 204. To adjust P_(R), acarrier-signal-to-noise-ratio, defined as C_(R)/(N_(R)+I_(R)), may becalculated using the current P_(R). The carrier signal C_(R) may be thepower received by the satellite 202 and calculated by an equationC_(R)=P_(R)−D_(R), where D_(R) is the dynamic degradation 324 of thechannel 302 and estimated at each time interval of a frame length. N_(R)and I_(R) may represent the estimated noise and interference to thecurrent P_(R), respectively, and may correspond to the staticdegradation 326 of the channel 302. I_(R) may also stem from other userterminals 204 that are concurrently exchanging signals with thesatellite 202. As these quantities may change slowly, they may beestimated at a time interval of multiple frame length.

The quality of the broadcasting signal from the satellite 202 may berepresented by a forwardlink-pilot-tone-signal-to-noise-ratio (or,equivalently, broadcasting-signal-to-noise-and-interference-level)S_(FP)/(N_(FP)+I_(FP)). S_(FP), N_(FP) and I_(FP) may be thebroadcasting signal intensity received by the user terminal 204, noise,and interference, respectively. These quantities may be measured by theuser terminal 204.

FIG. 4 is a schematic diagram 400 illustrating the returnlink powercontrol concept of the communication system shown in FIG. 2. A powermultiplier 402 of the user terminal 204 may receive a modulated signalthat may be a digitized signal of the user's voice, adjust the receivedsignal intensity based on P_(R) and send the signal to the satellite 202through a channel 302 (shown in FIG. 3). During the propagation throughthe channel 302, the signal may be subject to a channel fading 404 dueto the lengthy travel distance and other environmental sources, such astrees and clouds on the signal path. The signal may also be affected byco-channel interference (CCI) from the user terminals 204 that may usethe same channel (or, equivalently, frequency band) and by adjacentchannel interference (ACI) from the user terminals 204 that may use theadjacent channel.

Upon completion of signal processing in the satellite 202, thefeederlink transmission 308 may send the processed signal to the gatewaystation 206. Subsequently, the signal is processed by the firstdemodulator/decoder mechanism 406 of the gateway station 206. The firstdemodulator/decoder mechanism 406 may output the processed signal to aparty coupled thereto as indicated by an arrow 422. The firstdemodulator/decoder mechanism 406 may also check returnlink error (or,equivalently, Metric_(R)), determine the carrier-signal-to-noise-ratioC_(R)/(N_(R)+I_(R)) and send the ratio to a source coding 408. Thesource coding 408 may code the one bit dedicated to indicate the signalintensity of each frame, where the one bit may be sent to the userterminal 204 conforming to the CDMA2000 standard. The seconddemodulator/decoder mechanism 410 may combine the one bit data withother data input and send the combined signal to the satellite 202.Subsequently, the forwardlink transmission 316 may send the signal tothe user terminal 204 through the channel 302, where the signal may besubject to a channel fading 415, noises, and interferences.

The signal received by the user terminal 204 may be used by abroadcasting-signal-to-noise-ratio measurement tool 416 and ademodulator/decoder mechanism 412. The demodulator/decoder mechanism 412may subsequently decode the signal and output the decoded signal to theuser and to a source decoding 414. The signal received by the sourcedecoding 414 may include the one bit dedicated to indicate the signalintensity. The source decoding 414 may detect the returnlink error (or,equivalently, Metric_(R)) and send it to a power control algorithm 418.As will be explained later, the power control algorithm 418 may requirea broadcasting-signal-to-noise-ratio S_(PF)/(N_(PF)+I_(PF)) that may bemeasured by a broadcasting-signal-to-noise-ratio measurement tool 416.It is noted that a closed loop may be formed by a cycle of theinformation flow that may start from and end at the source decoding 414.Also, an open loop may be formed to provide the power control algorithm418 with the broadcasting-signal-to-noise-ratio, where the open loop maystart from the feederlink transmission 308 that sends a signal asindicated by an arrow 420 a to the power control algorithm 418 thatreceives the broadcasting-signal-to-noise-ratio as indicated by anarrows 420 b.

FIG. 5 is a functional block diagram 500 of the power control algorithm418 in accordance with one embodiment of the present invention. Thepower control algorithm 418 may comprise three portions: a portion forthe prediction of channel degradation D_(F) (fast components) thatincludes three blocks 502, 504 and 506; a portion for the prediction ofchannel noise plus interference (slow components) that includes threeblocks 506, 508 and 510; and a portion for updating model parametersthat includes a block 512.

The power control algorithm 418 may receive abroadcasting-signal-to-noise-ratio from the mechanism 416 at the block502 and a detected returnlink error from the source coding 414 at theblock 510. Then, a forwardlink carrier-signal-to-noise-ratioC_(F)/(N_(F)+I_(F)) and a returnlink carrier-signal-to-noise-ratioC_(R)/(N_(R)+I_(R)) may be estimated in the blocks 502 and 510,respectively. The block 502 may also receive a forwardlink power signalthat may be a constant signal. The forwardlink power signal may be basedon a statistical average of the previous broadcasting signals receivedby the user terminal 204. Then, C_(F)/(N_(F)+I_(F)) estimated in theblock 502 may be used in the block 504 to predict a fast changingforwardlink degradation D_(F). Subsequently, the predicted D_(F) may besent to the block 506 to compute a returnlink power signal P_(R) in theblock 506. The block 510 may receive the returnlink power signal P_(R)computed in the block 506 to form a closed feedback loop. The estimatedC_(R)/(N_(R)+I_(R)) in the block 510 may be sent to the block 508 topredict the change in slow changing returnlink noise N_(R) andinterference I_(R), which may be input to the block 506.

The block 512 may include two parameter models: forward and returnlinkcorrelation D_(R) prediction model (a fast model) 514 and N_(R)+I_(R)prediction model (a slow model) 516. Considering bit error ratio (BER)requirement, the fast and slow models may make adjustment to theprediction of D_(R) and N_(R)+I_(R) in the blocks 504 and 508,respectively.

The mathematical models and parameters implemented in the fast model 514and slow model 516 can be used for various transmission bandwidths andsystem application environments. The block 514 may estimate theweighting parameters to the forwardlink variation estimation applying tothe returnlink power weighting parameter. This block may adaptivelyadjust the correlation between the returnlink and the forwardlink. Usingthe past estimation history of the correlation data and the delayfeedback quality indication for the quality of the past power controlcalculation, the weighting parameter can be accurately estimated. Asimplified model for the adjustment can be done by using adaptivefilter, for example, mathematical models that are numerically stable andcomputationally accurate may be presented as following:

-   -   Estimation of D_(R), the fast change portion:        -   The update step time is a unit time. Let's assume the            internal estimation state is X_(D), which is needed to            provide one-step prediction. A mathematics expression of one            step prediction can be written as        -   X_(D)(t+1)=F_(D)(t+1|t)X_(D)(t)+G_(D)(t+1|t)(D_(DL)(t)−D_(DL)(t−1))+ω_(N)(t)        -   Y_(N)(t)=X_(N)(t)+ε_(N)(t)        -   D_(R)(t)=Y_(N)(t)+D_(R)(t−1)    -   Estimation of NI_(R) (=N_(R)+I_(R)) the slow change portion:        -   The update rate is Y (Y>X), which is need to provide k step            prediction (k>=1, k times of unit time)        -   X_(NI)(t+k)=F_(NI)(t+k|t)X_(NI)(t)+G_(NI)(t+k|t)(NI_(UL)(t)−NI_(UL)(t−1))+ω_(NI)(t)        -   Y_(NI)(t)=X_(NI)(t)+ε_(NI)(t)        -   NI_(R)(t)=Y_(NI)(t)+NI_(R)(t−1)

The notations in the above equations of Kalman filter are well known inthe art for adaptively parameter adjustment and, for simplicity,detailed description will not be given. It is noted that the presentinvention may be practiced with other conventional types of mathematicalmodels to compute D_(R) and NI_(R).

It is noted that, as the transmission frequency and the receivingfrequency are not exactly the same, the open loop measured variation ofa forwardlink power, which may be determined by the block 502, may notbe exactly the same with the variation of the returnlink power signalP_(R) emitted from the block 506. However, there may be a correlationbetween the forwardlink variation and returnlink variation. Thecorrelation may be closely related to the frequency separation betweenthe returnlink frequency and forwardlink frequency, related to theenvironment. The power control algorithm 418, more specifically theforward-and-return-link-correlation D_(R) prediction block 514, mayadaptively calculate the correlation using the delayed feedbackmeasurement.

FIG. 6 is a schematic diagram 600 illustrating an exemplary metricfeedback source coding in accordance with one embodiment of the presentinvention. The gateway station 206 may receive input frames 602 througheach channel and each input frame may be decoded to determine its BERmetric in a functional block 604. Then, a contiguous set of frames 601a-601 e may be selected, where the notation “t” in the input frames 602represents the (current) time when the present feedback source coding isperformed. In blocks 606 and 608, the average metric of the selectedfive frames 601 a-601 e may be calculated and encoded.

Table 1 shows an exemplary 5-bit source coding for the average metric,where each of the 5 bits may be stored in one of the five consecutiveoutput frames 610. As shown in the second column of Table 1, the firsttwo bits may be used as synchronization bits to identify the starting ofthe feedback bits while the other three bits may be used as informationbits. The synchronization bits may be carried by two frames 612 d and612 e before the current time “t” if the information bit is available.The first column of Table 1 represents the values represented by thethree information bits and the third column represents the correspondingaverage metric values. As the three information bits may be carried bythree consecutive output frames 612 a-612 c, the source coding methodmay generate a transmission process delay by a three-frame interval. InFIG. 6, only five frames 601 a-601 e is used to generate the average BERmetric. However, it should be apparent to those of ordinary skill thatthe present invention may be practiced with any number of frames.

TABLE 1 An exemplary source coding for a metric Value of informationbits Bit sequence Metric value 0 11000  0 1 11001 10 2 11010 18 3 1101124 . . . . . . . . . 7 11111 40

FIG. 7 is a plot 700 of BER vs. carrier-signal-to-noise-ratioillustrating that the power control cushion may directly impact to thesystem performance. In the perfect power control case, there is no needfor power control cushion. The BER requirement showing in 706 can bedirectly interpolated as line 710. However, in reality, a perfect powercontrol does not exist. The power may be controllable to be distributedin a region as the bell shaped curve, which may be approximatelyestimated as a Gaussian distributed function, like 716 with its meanrepresented by line 712. The power level can be, in turn, reflected tothe BER axis. So we have 718 reflect to 716 and 708 reflect to 712. Inthe plot, the average BER is still 706 (note that we have the scale inlogarithm). Instead of using the power showing in line 710, we have touse the power as indicated in line 712. The distance from 710 to 712 isthe power cushion. Curves 704 and 702 represent BERs as functions ofcarrier-signal-to-noise-ratio C/(N+I) before and after channel. Theabove analysis is to the results after channel coding. To reach the BERrequirement without channel coding may require a much high input powerlevel and larger power cushion. A high performance channel coding schememay reduce the required power control cushion. The abscissa mayrepresent C/(N+I) and considered to be proportional to a power level. Ascan be noticed by comparing the two curves 702 and 704, the BER at thesame power level may be reduced significantly by applying the channeldecoding technique. An improved channel coding technique may reduce therequirement of power control cushion. With a given channel codingperformance, the power control algorithm can further reduced the powercontrol cushion requirements.

The required BER 706 may be specific to each communication system, whilethe required C/(N+I) 710 may be determined by the required BER and thecurve 702. Ideally, the system should communicate at the required BER.However, in normal operations of the system, C/(N+I) may have adistribution 716 around an operational C/(N+I) point 712, where theoperational C/(N+I) point 712 may be higher than the required C/(N+I)710 to provide a power control cushion 714. Likewise, BER may have asimilar distribution 718 around the operational BER point 708. Analysisshows that an improvement of 1 dB (from 2 db to 1 db) in the powercontrol cushion 714 can double the system capacity.

FIG. 8 is a plot 800 of measured and averaged signals in accordance withone embodiment of the present invention. The abscissa and ordinate ofthe plot 800 may be the distance traveled by a user terminal 204 and thereceived signal intensity, respectively. The curve 804 representssignals measured by the use terminal 204 moving at the speed of 55 MPHwhile the curve 802 represents signals averaged over each frame.

FIG. 9A is a plot 900 of signals illustrating the effect of a powercontrol on an error signal in accordance with one embodiment of thepresent invention. The curves 902 and 904 represent the required powerbefore the power control is performed on the system 200 and the providedpower after the power control is performed, respectively. FIG. 9B is aplot of C/(N+I) distributions 910 in accordance with one embodiment ofthe present invention. The curves 912 and 914 that are similar to thecurve 716 represent C/(N+I) distribution with and without power control,respectively. As can be noticed, the C/(N+I) distribution 912 with thepower control is narrower, which can translate into a requirement of asmaller power control cushion and an enhanced system performance.

FIG. 10 is a flowchart 1000 illustrating exemplary steps for metricfeedback source coding in accordance with one embodiment of the presentinvention. In step 1002, the gateway station 206 may receive a pluralityof input signal frames 602. Next, the received input signal frames maybe decoded in step 1004. Then, for each of the decoded plurality ofinput signal frames, a metric may be calculated in step 1006.Subsequently, an average of the metrics may be calculated in step 1008.In step 1010, a sequence of bits comprising a plurality ofsynchronization bits and a set of information bits may be selected.Next, in step 1012, the plurality of synchronization bits may bepopulated by ones, while the set of information bits may be populated byan information bit sequence that represents the value of the calculatedaverage metric. Then, the populated sequence of synchronization bits andset of information bits may be sent to the satellite 202 in step 1014.

FIG. 11 is a flowchart 1100 illustrating exemplary steps for controllingthe returnlink power of a user terminal in accordance with oneembodiment of the present teachings. In step 1102, the user terminal 204may receive a broadcasting-signal-to-noise-ratio. Next, a forwardlinkcarry-signal-to-noise-ratio may be estimated using the receivedbroadcasting-signal-to-noise-ratio in step 1104. In step 1106,forwardlink degradation may be predicted based on the estimatedforwardlink carry-signal-to-noise-ratio. The user terminal 204 may alsoreceive an error of a returnlink signal in step 1108. Next, in step1110, a returnlink carrier-signal-to-noise-ratio may be estimated usingthe received error. Then, a noise and an interference of the returnlinksignal may be predicted in step 1112. In step 1114, a returnlink powersignal may be calculated using the predicted forwardlink degradation,noise level, and interference level.

It should be understood, of course, that the foregoing relates topreferred embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

1. A method for controlling a returnlink power of a user terminal, saidmethod comprising: receiving a broadcasting-signal-to-noise-ratio;estimating a forwardlink carrier-signal-to-noise-ratio based on thebroadcasting-signal-to-noise-ratio; predicting a forwardlink degradationbased on the forwardlink carrier-signal-to-noise-ratio; receiving anerror of a returnlink signal; estimating a returnlinkcarrier-signal-to-noise-ratio based on the error; predicting a noise andinterference of the returnlink signal; and calculating a returnlinkpower signal based on the forwardlink degradation, noise andinterference.
 2. The method of claim 1, further comprising: using thereturnlink power signal in the steps of estimating a returnlinkcarrier-signal-to-noise-ratio, predicting a forwardlink degradation, andpredicting a noise and interference.
 3. The method of claim 1, furthercomprising: estimating a set of model parameters to adjust the noise,interference, and a dynamic degradation.
 4. The method of claim 3,wherein the step of estimating a set of model parameters is based on aKalman filter.
 5. The method of claim 1, wherein the user terminal is acellular phone or a personal digital assistant.
 6. A method forcontrolling a returnlink power of a user terminal, said methodcomprising: receiving a broadcasting-signal-to-noise-ratio; estimating aforwardlink carrier-signal-to-noise-ratio based on thebroadcasting-signal-to-noise-ratio; predicting a forwardlink degradationbased on the forwardlink carrier-signal-to-noise-ratio; calculatingadaptively a conelation between a variation of forwardlink signal and avariation of the returnlink signal using a delayed feedback measurement;receiving an error of a returnlink signal; estimating a returnlinkcarrier-signal-to-noise-ratio based on the error; predicting a noise andinterference of the returnlink signal; calculating a returnlink powersignal based on the forwardlink degradation, noise and interference;using the returnlink power signal in the steps of estimating areturnlink carrier-signal-to-noise-ratio, predicting a forwardlinkdegradation, and predicting a noise and interference; and estimating aset of model parameters to adjust the noise, interference, and a dynamicdegradation based on a Kalman filter.
 7. The method of claim 6, whereinthe user terminal is a cellular phone or a personal digital assistant.8. A computer readable medium embodying program code with instructionsfor controlling a returnlink power, said computer readable mediumcomprising: program code for receiving abroadcasting-signal-to-noise-ratio; program code for estimating aforwardlink carrier-signal-to-noise-ratio based on thebroadcasting-signal-to-noise-ratio; program code for predicting avariation of forwardlink degradation based on a variation of theforwardlink canier-signal-to-noise-ratio; program code for receiving anerror of a returnlink signal; program code for estimating a returnlinkcarrier-signal-to-noise-ratio based on the error; program code forpredicting a noise and interference of the returnlink signal; andprogram code for calculating a returnlink power signal based on theforwardlink degradation, noise and interference.
 9. The computerreadable medium of claim 8, wherein said computer readable mediumcomprises program code for using the returnlink power signal in aprocess of executing the program codes for estimating a returnlinkcarrier-signal-to-noise-ratio, predicting a forwardlink degradation, andpredicting a noise and interference.
 10. The computer readable medium ofclaim 8, wherein said computer readable medium comprises program codefor estimating a set of model parameters to adjust the noise,interference, and a dynamic degradation.
 11. The computer readablemedium of claim 8, wherein the program code for estimating a set ofmodel parameters is based on a Kalman filter.
 12. The computer readablemedium of claim 8, wherein the user terminal is a cellular phone or apersonal digital assistant.
 13. A satellite communication system,comprising: a satellite; and at least one user terminal comprising: aforwardlink receiver configured to receive a forwardlink broadcastingsignal and a forwardlink user-data transmission signal from thesatellite; a returnlink power control configured to generate areturnlink power signal based on the forwardlink broadcasting signal andthe forwardlink user-data transmission signal; and a returnlinktransmission configured to send the returnlink power signal to thesatellite a gateway station configured to communicate with thesatellite, wherein the gateway station further comprises: a feederlinkreceiver configured to receive a first signal from the satellite; and afeederlink transmission configured to receive a metric and a pilot tunesignal power from the feederlink receiver and send a second signal tothe satellite, wherein the second signal is based on the first signal,the metric, and the pilot tune signal power.
 14. The satellitecommunication system of claim 13, wherein the at least one user terminalcommunicates with the satellite via a channel having a staticdegradation mechanism and a dynamic degradation mechanism.
 15. Thesatellite communication system of claim 14, wherein the staticdegradation mechanism is in out-space region.
 16. The satellitecommunication system of claim 14, wherein the dynamic degradationmechanism is in atmosphere.
 17. The satellite communication system ofclaim 13, wherein the at least one user terminal is a cellular phone ora personal digital assistant.
 18. A satellite communication system,comprising: a satellite; at least one user terminal configured tocommunicate with the satellite via a channel, said at least one userterminal comprising: a forwardlink receiver configured to receive aforwardlink broadcasting signal and a forwardlink user-data transmissionsignal from the satellite; a returnlink power control configured togenerate a returnlink power signal based on the forwardlink broadcastingsignal and the forwardlink user-data transmission signal; and areturnlink transmission configured to send the returnlink power signalto the satellite; and a gateway station configured to communicate withthe satellite comprising: a feederlink receiver configured to receive afirst signal from the satellite; and a feederlink transmissionconfigured to receive a metric and a pilot tune signal power from thefeederlink receiver and send a second signal to the satellite, whereinthe second signal is based on the first signal, the metric, and thepilot tune signal power.
 19. A method for controlling a returnlink powerof a user terminal, said method comprising: receiving a returnlink and areturnlink power; estimating a returnlink carrier-signal-to-noise-ratiobased on the returnlink error and returnlink power; predicting a noiseand interference of the returnlink power based on the returnlinkcarrier-signal-to-noise-ratio and the returnlink power; receiving aforwardlink power; estimating a forwardlinkcaffier-signal-to-noise-ratio based on the forwardlink power;calculating adaptively a correlation between a variation of theforwardlink power and a variation of the returnlink power; predicting aforwardlink degradation based on the forwardlinkcarrier-signal-to-noise-ratio, the correlation and the returnlink power;and computing a returnlink power based on the noise, the interferenceand the forwardlink degradation.
 20. The method of claim 19, furthercomprising: estimating a set of model parameters to adjust the noise,the interference, and a dynamic degradation based on a Kalman filter.21. The method of claim 19, wherein the user terminal is a cellularphone or a personal digital assistant.
 22. A computer readable mediumembodying program code with instructions for controlling a returnlinkpower, said computer readable medium comprising: program code forreceiving a returnlink error and a returnlink power; program code forestimating a returnlink carrier-signal-to-noise-ratio based on thereturnlink error and returnlink power; program code for predicting anoise and interference of the returnlink power based on the returnlinkcarrier-signal-to-noise-ratio and the returnlink power; program code forreceiving a forwardlink power; program code for estimating a forwardlinkcarrier-signal-to-noise-ratio based on the forwardlink power; programcode for calculating adaptively a correlation between a variation of theforwardlink power and a variation of the returnlink power; program codefor predicting a forwardlink degradation based on the forwardlinkcarrier-signal-to-noise-ratio, the correlation and the returnlink power;and program code for computing a returnlink power based on the noise,the interference and the forwardlink degradation.
 23. The computerreadable medium of claim 22, wherein said computer readable mediumcomprises program code for estimating a set of model parameters toadjust the noise, the interference, and a dynamic degradation.
 24. Thecomputer readable medium of claim 23, wherein the program code forestimating a set of model parameters is based on a Kalman filter.